The instant invention relates to a method for developing a latent image. U.S. Pat. Nos. 4,440,846 and 4,399,209 to The Mead Corporation describe an imaging system wherein a photosensitive layer comprising microcapsules containing a photosensitive composition in the internal phase is image-wise exposed to actinic radiation and subjected to a uniform rupturing force whereupon the microcapsules rupture and image-wise release the internal phase. An image-forming agent such as a substantially colorless color former is typically associated with the microcapsules such that when the microcapsules rupture the color former is able to image-wise react with a developer material and produce a color image. In the embodiments described in the aforementioned patents, the uniform rupturing force is pressure and the capsules are ruptured by passing the image-wise exposed sheet through the nip between a pair of pressure rollers. A comparatively large caldender nip is required for this purpose in order to establish a uniform linear pressure across the surface of the imaging sheet. As a general rule, as the width of the imaging sheet doubles, the diameter of the pressure rollers must cube to achieve uniform linear pressure and development.
In accordance with this invention latent images produced by image-wise exposure of the aforementioned sheet are developed by abrasion as contrasted with pressure. In accordance with a particular embodiment of the invention, a developer roll abrades the active coating on the color producing substrate to promote the reaction of the color forming ingredients.